When square wooden frame members are fastened together by conventional connecting elements consisting of sleeves which have the same cross-sectional shape as the frame members, problems arise when one or both of the frame members are twisted and must be fitted with both ends into said sleeves. In prior art constructions, the respective locations of sleeves opposite each other presupposes a frame member which is wholly or at least substantially without twist.
If the sleeves receiving the frame members are of square cross-section, both their inner height and breadth must be larger than the respective dimensions of the frame member, so as to provide enough play for a predetermined, sufficient degree of twisting in the frame members. The disadvantage of such construction is that it provides excessive play for straight frame members, which therefore are poorly fastened.
At the other extreme, when the sleeve is circular in cross-section, the square frame member can be twisted to an unlimited extent and still have support with its corners against the inner walls of the sleeve. In this case, however, the frame members will be difficult to lock in position, and their corners are likely to be damaged by wear and pressure.